We use high revving engines, so they should be changed more frequently than cars. I do 3,000 miles / 3 months, but on cars I go longer, like the manufacturer says.
I mention that because I use Supertech aka Walmart brand. Why? All natural oils ARE the same. People will give you voodoo and blackmagic reasons on why thats not so but I know better. Scientifically, synthetic oils are supreme because they last long, dont break down by heat like natural oils, but they still get dirty. Thats why I don't use it for my engine, because its a waste to change the synthetic oil every 3 months/3000 miles...you're not going to see the benefits of that choice and you might as well use natural oils. Walmart oil is the cheapest, and refined by the same people that make x,y,z.